1. Field of the Invention
The present invention relates to a frequency synthesizer circuit employing a phase-locked loop (PLL) circuit.
2. Description of the Related Art
As shown in FIG. 1, a frequency synthesizer circuit according to the related art used in portable telephones, etc., which frequency synthesizer generates an output signal in phase with an input signal, comprises a PLL circuit 101, which is a digital circuit, a voltage controlled oscillator (VCO) 102, which is an analog circuit, and a low pass filter (LPF) 103. The PLL circuit 101 and the VCO 102 are mounted on a single substrate 100. Terminals 101a, 101b, 102a, and 102b are formed on the substrate 100 and the terminals 101b, 102a are externally connected to the LPF 103.
In such a configuration, when a so-called wafer probing test operation for the VCO 102 is to be performed, a control voltage is provided from a probe of a testing device 200 connected to the (input) terminal 102a and an oscillation signal provided from the VCO 102 based on the provided control voltage is detected by a probe of the testing device 200 connected to the (output) terminal 102b. 
However, in order to respond to the demand for weight saving of the apparatus, nowadays, components configuring the frequency synthesizer circuit tend to be integrally mounted on a single substrate. Therefore, the frequency synthesizer according to the related art described above is also required to mount the PLL circuit, the VCO, and the LPF on a single chip.
The frequency synthesizer according to the related art may be reduced in the weight of the apparatus by mounting the components configuring the frequency synthesizer circuit on a single chip as mentioned above. However, in case when the frequency synthesizer circuit is integrated in the single chip, the input terminal 102a of the VCO is not exposed to the exterior. As a result, it is not possible to check an oscillation frequency provided from the VCO by the wafer probing test, which is performed on the frequency synthesizer circuit in a wafer status so as to determine if the VCO is working properly.
It is possible to devise exposing of the input terminal of the VCO to the exterior, but this cannot be adopted since even a small amount of leakage of noise components on the input terminal exposed to the exterior during an off-switch mode, i.e. non-testing mode, adversely affects the noise characteristic of the frequency synthesizer circuit. Therefore, it is preferable not to expose the input terminal of the VCO to the exterior in order to prevent the entering of the noise components into the frequency synthesizer circuit.
Also, it is possible to check the oscillation frequency provided from the VCO in the final test, which is performed after completing the assembly of the frequency synthesizer circuit into a final product such as a portable phone, etc., since a locked condition can be easily obtained by utilizing a closed loop of the PLL circuit in the frequency synthesizer circuit. However, the replacement cost occurring when detecting a defective chip in the final test, which is performed after the frequency synthesizer circuit is assembled into the final product, is significantly larger than that occurring when detecting a defective chip in the wafer probing test, which is performed on the frequency synthesizer circuit in a wafer status before the assembly of the frequency synthesizer circuit into the final product. Thus, it is preferable to check the oscillation frequency provided from the VCO in the wafer-probing test in terms of cost.
The present invention is directed to solve the above-mentioned problems and an object of the present invention is to provide a frequency synthesizer circuit, which can be easily tested by the wafer-probing test before the assembly of the frequency synthesizer circuit into a final product, without directly exposing a terminal of the VCO to the exterior.
The frequency synthesizer circuit according to the present invention includes a phase-locked loop circuit, a voltage controlled oscillator, a low pass filter, an input terminal for providing serial data provided from the exterior to the phase-locked loop circuit, an output terminal for providing an oscillation signal provided from the voltage controlled oscillator, and a testing unit providing a testing voltage with a binary value to the voltage controlled oscillator, wherein, the phase-locked loop circuit, the voltage controlled oscillator, the low pass filter, and the testing unit are mounted on a single chip, and usability of the frequency synthesizer circuit is determined based on the oscillation signal provided from the voltage controlled oscillator via the output terminal according to the testing voltage with a binary value provided from the testing unit.
According to the present invention, since the testing unit that provides the testing voltage with a binary value to the voltage controlled oscillator can be mounted integrally with the voltage controlled oscillator, the phase-locked loop circuit, and the low pass filter, the usability of the frequency synthesizer circuit can be determined based on the oscillation signal provided from the voltage controlled oscillator via the output terminal according to the testing voltage with a binary value provided from the testing unit, without exposing an input terminal of the voltage controlled oscillator to the exterior for connecting a probe of an external testing device. Therefore, it is possible to perform the oscillation frequency check on the frequency synthesizer circuit, particularly on the voltage controlled oscillator via the testing unit before assembling the frequency synthesizer circuit into the final product.
According to the present invention, if necessary, the testing unit may be provided between the low pass filter and the voltage controlled oscillator and the testing unit may provide the testing voltage with a binary value based on a control signal included in the serial data provided from the phase-locked loop circuit.
According to the present invention, since the testing unit may be provided between the low pass filter and the voltage controlled oscillator and the testing unit may provide the testing voltage with a binary value based on the control signal included in the serial data provided from the phase-locked loop circuit, the control signal included in the serial data may be provided from the input terminal to the testing unit via the phase-locked loop circuit and the usability of the frequency synthesizer circuit may be determined based on the oscillation signal provided from the voltage controlled oscillator via the output terminal according to the testing voltage with a binary value provided from the testing unit, without exposing an input terminal of the voltage controlled oscillator to the exterior for connecting a probe of an external testing device before assembling the frequency synthesizer circuit into the final product.
According to the present invention, if necessary, the testing unit may be provided in the phase-locked loop circuit and the low pass filter may be configured as a passive filter, wherein the testing voltage with a binary value provided from the testing unit may be provided to the voltage controlled oscillator via the low pass filter.
According to the present invention, since the testing unit may be provided in the phase-locked loop circuit and the low pass filter may be configured as a passive filter, the testing voltage may be provided to the voltage controlled oscillator via the passive filter, which is configuring the low pass filter, without directly connecting the testing unit to the voltage controlled oscillator.
According to the present invention, if necessary, the voltage controlled oscillator may provide the oscillation signal corresponding to a frequency band of a plurality of channels, the testing unit may switch a channel of the voltage controlled oscillator based on a channel selection signal provided from the phase-locked loop circuit, and the usability of the frequency synthesizer circuit may be determined based on the oscillation signal provided from the voltage controlled oscillator via the output terminal according to the testing voltage with a binary value provided from the testing unit.
According to the present invention, when the voltage controlled oscillator can provide the oscillation signal corresponding to a frequency band of a plurality of channels, the testing unit may switch the channel of the voltage controlled oscillator based on the channel selection signal provided from the phase-locked loop circuit, and therefore, the usability of the frequency synthesizer circuit may be determined based on the oscillation signal provided from the voltage controlled oscillator via the output terminal according to the testing voltage with a binary value provided from the testing unit and thus it may be possible to check the oscillation signal provided from the voltage controlled oscillator with respect to every channel to which the voltage controlled oscillator is adapted.
According to the present invention, if necessary, the phase-locked loop circuit may include a divider counter to divide a frequency of the oscillation signal provided from the voltage controlled oscillator and an output terminal, wherein the divided oscillation signal may be provided from the output terminal.
According to the present invention, since the phase-locked loop circuit may include a divider counter to divide the frequency of the oscillation signal provided from the voltage controlled oscillator and an output terminal, the divided oscillation signal may be provided from the output terminal. Therefore, the wafer-probing test may be performed using the divided oscillation signal, which has a lower frequency than the oscillation signal before being divided. This makes it significantly easy to carry out the wafer-probing test.